This invention relates to a fixture for disposing a material on an airfoil or in an airfoil for an axial flow rotary machine. The material is heated to liquefy the material and the material is flowed to passages in the airfoil where the material solidifies to block, for example, a coating from entering the passage or a laser beam from striking the interior of the passage as a cooling air hole is drilled through to the passage. The material is commonly referred to as xe2x80x9cfiller materialxe2x80x9d or xe2x80x9cblocking materialxe2x80x9d and is disposed on the interior or exterior of the airfoil. More particularly, this invention relates to a fixture for disposing filler material in passages in the airfoil, such as passages in a rotor blade or a stator vane, which are the relatively large supply passages or the relatively small passages which provide conduits from the supply passage to the interior or exterior of the airfoil. Although this invention was developed in the field of axial flow rotary machines, this invention has application to other fields where a material is heated to liquefy the material and is flowed thereafter to the article where the material is disposed on or in the article.
Airfoils for gas turbine engines are disposed in a flow path for working medium gases. Examples of such airfoils are turbine blades and turbine vanes. The airfoils are bathed in hot gases as the gases are flowed through the engine. Cooling air is flowed though main supply passages on the interior of the airfoil under operative conditions. Stator vanes are typically larger than rotor blades and the main supply passages for cooling air in a turbine vane are larger in volume than the supply passages in a rotor blade.
The cooling air is then flowed from these passages through the airfoil to keep the temperature of the airfoil within acceptable limits. Cooling air holes also extend from the interior to the exterior of the airfoil. These cooling air holes are typically called xe2x80x9cfilm cooling holes.xe2x80x9d The cooling air holes are small and may have diameters that are in a range of eleven to seventeen mils (0.011-0.017 inches). Cooling air is flowed from the passages on the interior of the airfoil through the cooling air holes the hot walls to the exterior surface of the airfoil. The cooling air provides transpiration cooling as the air passes through the wall and, after the air is discharged from the airfoil, provides film cooling with a film of air on the exterior. The film of cooling air provides a barrier between the airfoil and the hot, working medium gasses.
The holes are drilled in predetermined patterns and are contoured to ensure adequate cooling of the airfoil. One way to drill the holes uses a laser to direct a beam of coherent energy at the exterior of the airfoil. The intense radiation from the laser beam bums through the wall of the airfoil, leaving behind a hole which provides a satisfactory conduit for cooling air. As the laser beam penetrates through the airfoil wall into an interior cavity, the laser beam may strike adjacent structure on the other side of the cavity causing unacceptable damage to the airfoil. Accordingly, blocking material may be disposed in the cavity to block the laser beam from striking walls bounding the cavity after the beam penetrates through the airfoil wall.
One approach is to leave disposed within the airfoil the ceramic casting core around which the blade is poured during the manufacturing process. The ceramic core provides a suitable blocking material. The ceramic core is subsequently removed by well known leaching techniques. This approach is described in U.S. Pat. No. 5,222,617 entitled xe2x80x9cDrilling Turbine Bladesxe2x80x9d issued to Gregore, Griffith and Stroud.
Another example of a filler material used for blocking material is wax or a wax-like material. The material is melted so that it may easily flow into interior passages, such as the leading edge passage of the airfoil. The temperature of the molten material when heated above its melting point may exceed two hundred and fifty degrees Fahrenheit (250xc2x0). The molten material may be poured by hand or injected into the cavity or may even be sprayed or painted on the surface to be protected. However, the molten material may severely scald personnel working with the material. Moreover, the operation is time consuming if such material is poured by hand into the airfoil.
One example of a wax-like blocking material which uses an additive to avoid forming voids is discussed in U.S. Pat. No. 5,049,722, issued to Corfe and Stroud, entitled xe2x80x9cLaser Barrier Material And Method Of Laser Drilling.xe2x80x9d In Corfe, a PTFE (polytetrafluoroethylene) wax-like material is disposed in a wax base. The PTFE helps avoid the formation of voids.
Still another approach is to use a masking agent, such as an epoxy resin, which is disposed in the airfoil in a fluid state. The epoxy resin is disposed in the airfoil by simply pouring the resin into the airfoil. The epoxy resin is at room temperature and poses no scalding hazard to personnel. The epoxy resin is further processed to harden the fluid and cause it to become a more solid material similar to the PTFE wax mentioned in U.S. Pat. No. 5,049,722. However, the resin is relatively viscous compared to molten wax and has difficulty in flowing through small connecting passages on the interior of the airfoil.
Another approach is to use a thixotropic medium that includes material for dispersing laser light. This approach is discussed in U.S. Pat. No. 4,873,414 issued to Ma and Pinder entitled xe2x80x9cLaser Drilling of Componentsxe2x80x9d. A particular advantage of this medium is that the dispersant material emits light when contacted by the laser light. Monitoring the light provides a method of detecting the presence of the laser beam as the laser beam breaks through the surface of the article and controlling the beam by using a feedback control to determine whether or not the laser beam has drilled a through hole. In addition, the viscosity of the medium is decreased by forcing the medium through a nozzle for lowering the viscosity of the medium so that the medium flows readily over an inner surface of the component.
Another approach is shown in U.S. Pat. No. 5,140,127 entitled xe2x80x9cLaser Barrier Materialxe2x80x9d issued to Stroud and Corse. This approach uses an injectable barrier material which is a composition selected from the group consisting of a first copolymer of tetrafluoroethylene and hexfluoropropylene and a second copolymer having a polytetrafluoroethylene backbone and a least one fluorinated alkoxy side group. The material is poured or injected into the interior of the component.
Another approach is shown in U.S. Pat. No. 5,767,482 entitled xe2x80x9cLaser Barrier Material and Methodxe2x80x9d issued to Turner. Turner uses finely divided crystalline material such as sodium chloride (salt), or other metal salts which are thermally stable and possess a high melting point. Salt may be introduced into the interior of a component by pouring or by making it a paste with water and injecting it. The salt is removed by washing the component with water.
The above art notwithstanding, scientists and engineers working under the direction of Applicants Assignee have sought to develop materials, methods, and devices for disposing a filler material in or on an article, such as for blocking a laser beam on the interior of airfoils which are useable for mass production operations and that provide for relatively easy removal from the article without performing several time consuming operations.
This invention is in part predicated on the recognition that fixtures used with polymer filler material that is heated to liquefy the material in mass production operations may provide significant production advantages by reducing the time needed to fill articles. The term xe2x80x9cheatedxe2x80x9d refers to raising the temperature of the material whether by the transfer of heat or by doing work on the material, such as forcing the material through a nozzle. These fixtures may be used, for example, for filling the interiors of airfoils for gas turbine engines with a blocking material for a laser beam. This invention is also in part predicated on the realization that heating such filler material for disposing the material on an exterior surface or in a relatively large internal volume of an article may result in the material unacceptably pulling away from the article as the filler material cools and contracts. It is also predicated in part on realizing that adhering a filler material to such an article may reduce or avoid having the material pull away and, concomitantly, may have a beneficial effect when performing laser drilling operations on an article such as an airfoil. This invention is also predicated in part on the realization that some airfoils, such as stator vanes, may require fixtures that engage the stator vane with a relatively soft material that resiliently deforms to accommodate tolerance variations at faying locations engaged by the fixture. This may occur because the location has not been finally machined until after the cooling holes are drilled. It is also predicated on recognizing that the filler material may bond so well to the soft material that separating the fixture from the airfoil may unacceptably remove portions of the filler material from the airfoil. This invention is also predicated in part on the recognition that having an unheated supply passage in a fixture for receiving and supplying a heated filler material that adheres to an airfoil may result in plugging the supply passage if the flow of the filler material is interrupted for even short periods of time such as occurs during the sequential filling of airfoils. In addition, it is also predicated on the realization that the pressure an injection means may apply to the filler material may not exceed levels needed to clear the plug because of limitations in delivery pressure imposed by the construction of the machine or limitations in delivery pressure imposed by the difference in pressure between the interior and exterior of the airfoil that the airfoil walls can tolerate. It is also predicated in part on realizing that decreasing the spanwise length of the adhering of the plug of filler material decreases the pressure needed to remove the plug. Finally, it is predicated in part on the realization that flowing a small volume of cured or partially solidified filler material which might adhere to the walls of the passage will provide acceptable results in a filled airfoil providing that the volume of filler material in which the small plug of filler material is disposed downstream of the passage will supply enough heat to remelt the filler material or soften the filler material provided that the filler material flows to a region in or adjacent to the airfoil that has a sufficient volume of new, heated filler material with sufficient thermal capacitance to remelt the plug.
According to the present invention, a fixture for flowing a stream of heated filler material to an article includes a tool member for resiliently engaging the article to form a containment region for the filler material at the article and includes a nozzle adaptor extending in the tool member for providing a sealing surface for the nozzle and a passage for filler material downstream of the sealing surface which is at a location that is nearer to the containment region than to any point that is located upstream of the tool member.
In accordance with one embodiment of the present invention, the article is an an airfoil, such as a stator vane or rotor blade
In accordance with one embodiment of the present attention, the fixture includes a sprue plate which extends laterally to engage the tool member and the nozzle adaptor is part of a sprue plate.
In accordance with one detailed embodiment, a masking material is disposed in the containment region to block the filler material from contacting the tool member.
In accordance with one detailed embodiment, the masking material extends from the containment region and circumferentially about the nozzle adaptor and between the nozzle adaptor and the tool member.
A primary feature of the present invention is a fixture for flowing a stream of pressurized filler material from a nozzle to an article, the fixture having a tool member formed of softer material than the article for resiliently engaging the article. Another feature is a containment region for receiving filler material which is bounded by the tool member and the article. Still another feature is a passage which extends through the tool member for flowing the filler material to the containment region. Another feature is a second member which has a portion of the passage. The second member has a sealing surface for engaging the nozzle which is formed of a harder material than the tool member. The sealing surface is nearer to the containment region than to any point upstream of the tool member. In one embodiment, a feature is an opening in the tool member which adapts the tool member to receive the nozzle. In one embodiment, the second member is a sprue plate. The sprue plate has a nozzle adaptor which extends into the tool member and has the sealing surface which is adapted to receive the nozzle. In one embodiment, a feature is an opening in a portion of the sprue plate through which a nozzle extends for engaging the nozzle adaptor.
A primary advantage of the present invention is the reduced cost and efficiency that results from repetitively filling articles with a filler material from a nozzle using a fixture that resiliently accommodates tolerance variations in the article with one material and has a harder sealing surface in close proximity to the article. Another advantage is the speed and cost of sequentially filling airfoils through a fixture with an adhesive filler material by avoiding blockages in a passage through the fixture that must be removed manually by the operator. In one embodiment, an advantage is the cost and quality of laser drilled holes in an airfoil which results from using a heated, adhesive filler material as a laser blocking material and having the ability to repetitively deliver the adhesive filler material to airfoils in quantity.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of the invention and the accompanying drawings.